Gas Viscosity Control
Sealed MEMS enclosures regulate internal gas pressure to control mechanical damping on resonating microstructures. Vacuum cavity dampening uses residual gas molecules inside a micro-cavity to absorb kinetic energy from moving proof masses. Contrived internal cavity pressure sets mechanical quality factor values for resonant sensors like gyroscopes and micro-mirrors.
Controlling gas viscosity prevents erratic structural oscillation and over-damped dynamic response.
Quality Factor
Low internal cavity pressure reduces squeezefilm and Couette gas damping on moving structures. Lowering gas damping increases sensor quality factor values, improving mechanical sensitivity and reducing drive power requirements. Resonant gyroscopes operate in high vacuum environments to achieve high mechanical amplification factors.
Accelerometers use controlled sub-atmospheric pressures to achieve critical damping, preventing structural ringing under transient shocks.
Outgassing Drift
Material outgassing from internal cavity walls and packaging adhesives degrades vacuum levels over operational lifespans. Residual gas pressure increases raise squeeze film damping, lowering the mechanical quality factor over time. Quality factor decay alters sensor scale factor calibration and dynamic bandwidth characteristics.
Getter materials deposited inside package cavities absorb outgassed species to maintain stable vacuum levels over time.
Factory Inspection
Quality control verifies package hermeticity using helium mass spectrometer leak detection systems. Resonance testing measures quality factor values on completed sensor assemblies to confirm internal cavity pressure levels. Automated qualification standards reject packages exhibiting quality factor drift beyond defined tolerance bands during thermal aging tests.
